Most motor vehicles have a manually operated parking brake which is operated by either a hand lever or a foot pedal. In a hand operated parking brake, the parking brake actuator is connected to a hand lever and to a cable which, in turn, is connected to the parking brake itself. The parking brake actuator sets the parking brake by pulling on the cable in response to someone pulling on the hand lever. The actuator applies tension to the cable to set the brake. Releasing the tension in the cable releases the parking brake. The actuator is released through moving the hand lever.
Conventionally, a parking brake actuator is either a ratchet-pawl mechanism, or a spring or tension spring-clutch mechanism.
The ratchet-pawl mechanism and the tension spring-clutch mechanism used for parking brake actuators have a number of drawbacks. Because a pawl and a ratchet are dependent upon tooth spacing for engagement, the operator must overtension the brake cable to avoid cable slack when setting the brake. Noise is also an issue as the pawl moves over the ratchet or sector gear as the operator sets the brake. The spring-clutch drawback is the large amount of tolerance in the mechanism resulting in a wide spread of tension on the brake cable. Breakage of the binding ends of the torsion spring is also a problem. Both of these actuators use several separate components to release the brake.